Various types of backup tongs have been devised over the past 50 years, including both manually operated and power operated backup tongs. U.S. Pat. No. 4,574,664 discloses an hydraulically powered backup tong with a pair of hydraulic cylinders which pivot the cage plate to move a pair of heads into an out of gripping engagement with the tubular. U.S. Pat. No. 5,778,742 discloses another version of the backup tong with a pair of hydraulic cylinders which pivot a pair of arms into and out of gripping engagement with the tubular.
Many backup tongs have a geometry which allows for only a narrow set of tubular diameters to be inserted into the open throat of the backup tong. Other backup tongs provide a circumferential combined coverage of the dies which grip the tubular which is significantly restricted, thereby tending to crush the tubular upon gripping and also reducing the friction surface for torque restraint, which tends to mark the tubular. Dies which pivot concentrate reactive forces on the pivot pin, and do not uniformly spread the forces to all dies. Pivoting heads or dies also tend to have alignment problems with the full range of tubular to be gripped by the heads or dies.
Other backup tongs have a design which utilizes a relatively long stroke for the hydraulic cylinders, thereby increasing the overall size of the backup tong. Some backup tongs employ a latching mechanism to close the open throat which is complex and thus costly to manufacture and difficult for an operator to use.
The disadvantages of the prior art were overcome by the present invention, and an improved backup tong and method of securing a tubular against axial rotation is hereinafter disclosed.